a
: a narrow elongated tract extending from a focus of suppuration and serving for the discharge of pus
b(1)
: a cavity in the substance of a bone of the skull that usually communicates with the nostrils and contains air
(2)
: a channel for venous blood
(3)
: a dilatation in a bodily canal or vessel
c
: a cleft or indentation between adjoining lobes (as of a leaf or corolla)
Examples of sinus in a Sentence
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Levoit Top Fill Humidifier The best-selling Levoit humidifier skillfully combats the dry air in my home, which really helped during the colder months when my skin and sinuses suffer most.
—
Toni Sutton, People.com, 11 July 2025
Saline irrigation uses a saline solution (a mixture of salt and water) to clear allergens, mucus, and bacteria from the nasal and sinus passages.
—Mark Gurarie, Verywell Health, 8 July 2025
What are micro-robots for sinus infection treatment?
—Kurt Knutsson, FOXNews.com, 7 July 2025
Many persistent sinus infections involve biofilms – colonies of bacteria that group together to resist efforts to kill them.
—New Atlas, 30 June 2025
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Toni Sutton, People.com, 11 July 2025
Saline irrigation uses a saline solution (a mixture of salt and water) to clear allergens, mucus, and bacteria from the nasal and sinus passages.
—Mark Gurarie, Verywell Health, 8 July 2025
What are micro-robots for sinus infection treatment?
—Kurt Knutsson, FOXNews.com, 7 July 2025
Many persistent sinus infections involve biofilms – colonies of bacteria that group together to resist efforts to kill them.
—New Atlas, 30 June 2025
See All Example Sentences for sinus
Cite this Entry
“Sinus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/sinus. Accessed 19 Jul. 2025.
Copy CitationKids Definition
Medical Definition
sinus
noun
si·nus
ˈsī-nəs 
: a cavity or hollow in the body: as
a
: a narrow elongated tract extending from a focus of suppuration and serving for the discharge of pus
a tuberculous sinus
b(1)
: a cavity in the substance of a bone of the skull that usually communicates with the nostrils and contains air
(2)
: a channel for venous blood
(3)
: a dilatation in a bodily canal or vessel
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